Thermal alteration experiments on organic matter from recent marine sediments in relation to petroleum genesis

Three fractions of organic matter: lipid (benzene:methanol-extractable), humic acid (alkali-extractable) and kerogen (residue) were extracted from a young marine sediment (Tanner Basin, offshore southern California) and heated for different times (5–116 hr) and temperatures (150°–410°C). The volatile (gases) and liquid products, as well as residual material, were then analyzed. On a weight basis, the lipid fraction produced 58% of the total identified n-alkanes, the kerogen fraction 41%, and the humic acid 1.0, those produced by thermal alteration of kerogen display a CPI < 1.0. The volatiles produced by heating the lipid and humic acid fractions were largely CO 2 and water, whereas those produced from heated kerogen also included methane, hydrogen gas and small amounts of C 2–C 4 hydrocarbons. A mechanism for hydrocarbon production due to the thermal alteration of organic constituents of marine sediment is discussed.